The extended air defense system has been analyzed. The Particular attention is paid to the threat of the air defense
system to cruise missile. A method named Threat Coefficient Method was proposed based on the analysis of the air
defense system structure and its operations. A threat coefficient model of the air defense system was built. It is shown
that the threat coefficient will be reduced while threat-length is reduced by using the model. The threat-length has been
researched based on radar theory. The method has been verified by means of simulation. Based on the analysis, it is
found that reducing the RCS or increasing active chaff could reduce the threat coefficient.